A base material assignment can be used in areas of the design, which are made from supplier material ‘as received’ without changing its microstructure, e.g. forming, welding, heat treatment. In these areas the “base material” strength values are valid.
A base material study in the LIMIT® fatigue analysis software will directly use the stresses from the FEA analysis for the assessment.
Since in most strength assessment problems it is valid to assume, that the crack initiation or the areas of yielding are located on the surface of the component of interest, the 3D stress tensor can be transformed to a 2D stress tensor in a plane tangential to the surface. This information is used for the assessment of the base material. For static assessments usually an equivalent stress value, such as the VonMises stress or the maximum principal stress, is used. However, the LIMIT® fatigue analysis software also offers additional stress measures, such as Normal Stress, Scaled Normal Stress (this stress type uses the normal stress in the section plane and scales it depending on the multiaxiality of the stress state and material parameters such as the ratio of fatigue strength for normal and shear stress) or code specific stress measures